I think the sounds are getting better. No, it doesn't sound like I'm sitting in a real car, but it's getting better. You have to remember that these sounds are generated, not sampled. Most other games have sampled sounds. They drive a real car around at different rpms and record the sound, then replay them similar to CSR.
Also, you have to consider the gaming environment. If you have a really loud computer, crappy speakers, etc, the game is going to sound crappy. If you have a dead-quiet pc, a well setup room, and a good sound card and speakers that have been tuned to the room, the game is going to sound like what the devs want it to.
Things are better, and they'll keep getting better. The game is still at version 0.5, not 10.5...if not the most realistic looking or sounding, it's definitely the best driving. Look at what the devs have done so far, and just think what it'll be like 2 years from now...